1. Field of the Invention:
This invention relates to a web tension meter for measuring the tension of a web of material, an object material to be examined, with the meter kept not in contact with the web, and a web tension controller adapted to control a means for regulating the web tension, in accordance with a suitable signal based on the level of the web tension measured by the web tension meter. For example, a web, a material to be examined, which is subjected to these measurement operations, consists of a web moved along a guide member between a paper feed unit and a folding unit in a rotary press.
2. Description of the Prior Art:
The prior art web tension meters applied to a web moved along a guide member in a rotary press include a web tension meter in which a web tension is measured by a differential transformer attached to a guide roller, and a web tension meter in which a web tension is measured by determining a quantity of displacement of a floating roller, one of guide rollers, as a quantity of turning movement of a displacement support shaft, as disclosed in, for example, Japanese Utility Model Laid-open No. 17159/1988. This publication also discloses web tension controllers applied to a web and using these web tension meters.
There is another prior art web tension meter (refer to the specification of U.S. Pat. No. 4711133) applied to a material to be examined, in which a pressure gas is supplied into a hollow chamber, which is opened in a position slightly away from a material to be examined, from the rear side of the same chamber, a gas pressure in a position at the edge of the opening of the hollow chamber and in the vicinity of the material being measured via an annular opening, which is provided so as to surround the previously-mentioned opening, and a hollow chamber communicating with this annular opening, whereby the tension of the material is determined.
These prior art web tension meters have their respective problems.
First, in the web tension meter disclosed in Japanese Utility Model Laid-open No. 17159/1988, in which a web tension is measured by a differential transformer attached to a guide roller, it is necessary that three rollers be installed for the measurement of a web tension, and the necessity of securing a space for the installation of the rollers impedes the designing of the meter. If the differential transformers are provided on the support portions at both sides of the measuring rollers, the imbalance of a web tension in the widthwise direction of a web can be measured to a certain extent. However, in a case where a web is passed in a laterally biased state around the measuring rollers, it becomes difficult to measure this imbalance.
The web tension meter disclosed in the same publication and adapted to measure a quantity of displacement of a floating roller as a quantity of turning movement of a displacement support shaft does not require the web tension measuring means provided in the above web tension meter using a differential transformer, so that it is free from design restrictions. However, the quantity of turning movement of the displacement support shaft cannot be varied at both sides, and, therefore, the imbalance of web tension in the widthwise direction of the web cannot be measured.
In the web tension meters disclosed in U.S. Pat. No. 4711,133, the problems in the above two examples disclosed in Japanese Utility Model Laid-open No. 17159/1988 are solved. However, the measuring head in this patent consists of a fixed member, a slide member adapted to be displaced slidingly with respect to the fixed member, and an urging member disposed between the fixed member and slide member, and it is necessary that the hollow chamber opened at one side of the slide member, the annular opening surrounding the opening of the hollow chamber and used to measure the gas pressure in a position on the side of the edge of this opening and in the vicinity of a material to be examined, and the hollow chamber communicating with the annular opening be provided separately. This causes the construction of the web tension meter to become complicated, and results in an increase in the price of the meter and maintenance troubles.